As a method of cooling a piston for an internal combustion engine, which is subject to heavy heat load during an engine operating condition, various measures have been taken. As one of the cooling measures, for instance, it is disclosed in the following Patent Document 1.
This piston is formed as an integral member with, for instance, aluminum alloy material, and provided with a plurality of cooling fins that are formed integrally with a back surface side opposite to a crown surface of a crown portion and protrude from the back surface of the crown portion. The cooling fins, which are located on the substantially middle side on the back surface, are formed into a substantially linear shape, while the cooling fins, which are located on an outer circumferential side of the middle side-cooling fins, are formed into an arc shape so as to surround the middle side-cooling fins.
A surface area of the back surface side of the crown portion is increased by the plurality of cooling fins formed integrally with the piston, then a cooling effect during a piston drive is increased.